This invention relates to an antifouling composition and more particularly to a rubber based antifouling coating capable of maintaining a preferred pigmentation and being acoustically transparent.
Various types of marine organisms which become attached to the submerged surfaces of ships cause increased drag effects and thus contribute to increased fuel consumption and overall speed reduction. Such organisms also tend to increase ship noise and adversely affect the operation of acoustical devices such as sonar domes and sonar shields by attaching themselves thereto and providing a source of background noise. For example, sonar domes are often provided with smooth rubber surfaces and when affixed thereto, the marine organisms not only destroy the surface integrity of the domes but also provide sites which tend to deflect and scatter the sonar beams. Also, the effectiveness of sonar shields designed to absorb and attenuate sonar beams is reduced by organisms which reflect the incoming sonar beams.
To prevent the accumulation of various marine organisms on rubber and metal substrates attention has been directed toward developing an antifouling coating having a high degree of flexibility and stability, which remains acoustically transparent over the useful life of the coating. For example, U.S. Pat. No. 3,033,809 generally discloses an antifouling coating employing a polyisobutylene polymer and an antifouling agent such as cuprous oxide or mercury compounds including mercuric oxide and mercurous chloride. However, as noted in the abovementioned patent, copper based antifoulants and pigments have a deleterious action on rubber substrates. Additionally, it was found that metal salts and oxides of copper and mercury compounds corrosively react with various metals and alloys.
An additional feature of the present invention not addressed by the prior art is the provision of a camouflage pigment for an antifouling coating which retains its coloration over the useful life of the coating. Copper antifoulants and pigments react with various other paint ingredients and chemical species in seawater such that a characteristic copper coloration eventually pervades the coating and renders the coating unsuitable for most camouflage purposes.